Antifoggants and stabilizers for photographic silver halide emulsion



ANTIFOGGANTS AND STABILIZERS FOR PHOTO- GRAPHIC SILVER HALIDE EMULSION Fritz Dersch and Millet R; De Angelus, Binghamton,

N.Y., assignors to General Aniline & Film Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed June 5, 1957, Ser. No, 663,577

6 Claims, (Cl. 96-109) The present invention relates to the employment of compounds which serve as antifogging and stabilizing agents for photographic silver halide emulsions and, more particularly, to the use of carboxyalkyl-a-tetrazole thio others, their esters and salts.

It is known that light-sensitive photographic emulsions such as gelatin silver halide emulsions have a tendency to fog. Fogging is caused in a number of Ways as, for example, by excessive ripening of the emulsions, during storage of the film or paper particularly at elevated temperatures and humidity, or by prolonged development.

Eiforts have been made to decrease or inhibit the tendency of the photographic emulsions to fog by adding thereto antifogging or stabilizing agents for the purpose of stabilizing or controlling the keeping qualities of the emulsions. Compounds particularly recommended for this purpose are mercapto tetrazoles or their disulfides or tetrazoles containing at least one imino group, the hydrogen atom of which is capable of substitution by silver. Although these compounds do have the ability to reduce the fog tendencies and to improve the stability of the emulsions, they have certain shortcomings, particularly in that they lower the sensitivity of the emulsions and, in some instances, reduce the optical or dye sensitivity thereof. These compounds, therefore, do not partake of the optimum characteristics for the purpose in view.

We have now discovered a class of stabilizers or fog inhibiting agents which not only prevent the formation of chemical fog in silver halide emulsions but, most imwherein R is hydrogen; alkyl such as methyl, ethyl, propyl, butyl, amyl, allyl, carboxymethyl, carboxyethyl, oarboxypr opyl, hydroxyethyl, hydroxypropyl and the like; aryl such as phenyl, toluyl, naphthyl, carboxyphenyl, sulfophenyl, methoxyphenyl and the like, or aralkyl such as benzyl and the like; R has the values given for R and, in addition, maybe a cation such as sodium, potassium, silver or the like; and n is a whole number of from 1 to 3.

rates Patent "ice Examples of compounds within the above formula which wehave found suitable for our purposes are:

(l) 1'phenyl-tetrazolyl-S-mecapto-acetic acid, its sodium,

potassium or silver salt (2) l-phenyl-tetrazolyl-5-mecapto-methyl acetate (3) l ethyl tetrazolyl 5 mercapto-acetic acid and its sodium, potassium or silver salts (4) 1-ethyl-tetrazolyl-mercapto-phenyl acetate (5) 1-phenyl-tetrazolyl-mercapto-propionic acid and its sodium, potassium and silver salts (6) l-propyl-tetrazolyl-S-mercapto-propionic acid (7) 1-carboxyethyl-tetrazolyl-S-mercapto-propionic acid (8) 1-phenyl-tetrazolyl-S-mercapto-methyl propionate (9) 1-phenyl-tetrazolyl-S-mercapto-butyric acid and its sodium, potassium and silver salts (10) 1-benzyl-tetrazolyl-S-mercapto-acetic acid (11 1-phenyl-tetrazolyl-mercapto-phenyl propionate' The above compounds are prepared by refluxing a 5- mercapto-tetrazole containing in the 1-position a suitable alkyl, aryl or aralkyl group as above with a bromoaliphatic acid such as bromo-acetic acid, ,B-bromo-propionic acid or 'y-bromo-butyric acid with an acid binding agent such as sodium hydroxide, pyridine or the like. After the reaction mixture is cooled, it is acidified and the solid which separates is collected by filtration.

The free acids so obtained may be converted into the desired salts by reaction with a water soluble compound of the cation to be introduced, such as potassium carbonate, sodium carbonate, silver nitrate or the like.

The esters are also prepared from the free acids by conventional methods. Typically, the free acid may be refluxed with the desired alcohol such as methyl, propyl or benzyl alcohol or a phenol inthe presence of hydro chloric acid.

Fog reduction may be obtained by use of the above compounds when solutions thereof are incorporated in the silver halide emulsions as ripening finals or as coating finals. By ripening finals is meant an addition made during the. ripening or sensitivity-increasing stage of the emulsion making process. Such additions may be made before, during or after the addition of the soluble silver salt such as silver nitrate to the soluble halide such as potassium bromide in the presence of a suitable colloid such as gelatin, PVA or solubilized casein.

By coating finals is meant an addition made to the emulsion just prior to coating it on a suitable support, i.e., glass, paper, film or the like, when the emulsion has nearly obtained its maximum sensitivity.

- When the compounds are used as ripening finals, it is recommended that they be employed in a concentration of /2 to 5 mg; per .4 mole of silver halide and when used as coating finals in a concentration of 5 to 300 mg. per .4 mole of silver halide. It is to be emphasized, however, that the concentration used depends very much onthe, type of emulsion which'is employed and it is advisable to determine the optimum concentration from case to case. In some instances, it is advantageous to apply this group of antifoggants and stabilizers in adjacent layers, that is, in a separate undercoating layer or in the anti-abrasion gelatin surface. In still other instances, it is desirable to apply them in one or all pro cessing baths or in preand post-processing baths.

The involved antifogging agents are useful with any kind of photographic emulsion, e. g., non-sensitized emulsions, orthochromatic, panchromatic, X-ray emulsions, paper emulsions and color emulsions. They may be used alone or with other antifoggants or stabilizers or in combination with sulfur, reductionand metal-sensitizers or with compounds containing hydroxypolyethenoxy groups, i.e., reaction products of a1cohols,'amines,, phenols. and the like with ethylene oxide;

The invention will be further illustrated by the following examples, although it is to be understood that the invention is not restricted thereto.

Example I A silver halide emulsion in gelatin containing 4% silver iodide and 96% silver bromide was prepared in a conventional manner and brought up to its maximum light sensitivity. It was then readied for coating and finals were added such as sensitizing dyes, stabilizers, and hardeners. A 1% solution of l-phenyl-tetrazolyl-S- Inercapto-acetic acid was prepared and added to the emulsion as an antifoggant and additional stabilizer. The emulsion contained about 0.4 mole of silver halide. The so prepared emulsion was coated on a suitable cellulose ester base and dried. Samples of these film coatings were then exposed in a Type IIB Sensitorneter and developed in a developer of the following composition:

The 1-phenyl-tetrazolyl-S-mercapto-acetic acid was prepared as follows: I

5 grams of 1-phenyl-5-mercapto-tetrazole, 3.90 grams of bromo-acetic acid and 30 ml. of 2 N NaOH were heated under reflux for two and one-half hours. After cooling, the reaction mixture was acidified with dilute hydrochloric acid, using Congo red paper as an indicator. A white solid was collected, dissolved in a minimum of ethanol and decolorized with Norite. Crystallization was efiected by the addition of water. The product was recrystallized from ethanol-water and dried. The yield was 3.1 grams. The melting point was 97-98 C.

Example 11 A silver halide emulsion in gelatin containing 4% silver iodide and 96% silver bromide was coated on film base in a manner known to the art. After the coating was performed, an aqueous gelatin solution containing 20 grams of gelatin per liter and 200 mg. of l-phenyl-tetrazolyl-S-mercapto-acetic acid was coated thereon as an anti-abrasion layer. After drying, film samples were exposed and processed as described in Example I. The samples described exhibited a relative speed of 100 and a fog of .20 compared with a type coating of the same emulsion having an anti-abrasion layer similar to that described above, but lacking the antifoggant and having a speed of 100 and a fog of .30.

Example 111 Exposed samples of a photographic film were devel- Example IV l The procedure is the same as in Example I excepting that the 1-phenyl-tetrazolyl-5-rnercapto-acetic acid was replaced by an equivalent quantity of l-phenyl-tetrazolyl- 5-mercapto-propionic acid.

The above compound is prepared in the same way as the compound of Example I but while using .028 mole of fi-bromo-propionic acid in lieu of the same quantity of bromo-acetic acid.

Example V The procedure was the same as in Example 1 excepting that the l-phenyl-tetrazolyl-S-mercapto-acetic acid was replaced by an equivalent quantity of the methyl. ester thereof.

Example VI The procedure was the same as in Example II excepting that the 1-phenyl-tetrazolyl-5-mercapto-acetic acid was replaced by an equivalent quantity of l-phenyl-tetrazolyl-S-mercapto-butyric acid or the silver salt thereof.

Modifications of the invention will occur to persons skilled in the art and we, therefore, do not intend to be limited in the patent granted except as necessitated by the appended claims.

We claim:

1. Light-sensitive photographic material comprising a base and a light-sensitive silver halide emulsion layer thereon, a layer of said photographic material containing as an antifoggant a compound of the following formula: v

wherein R is selected from the class consisting of hydrogen, alkyl, aryl and aralkyl; R' is selected from theclass consisting of alkyl, aryl, aralkyl and a cation; and n is I a whole number of from 1 to 3.

4. The article as defined in claim 3 wherein the antifoggant is 1-phenyl-tetrazolyl-5-mercapto-acetic acid.

5. The process of preventing fog formation in lightsensitive photographic materials comprising a base and a light-sensitive silver halide emulsion layer thereon, which comprises exposing said material and developing the same in the presence of a compound having the following structure:

N ll ll C-S(CH2)nCO OR wherein R is selected from the class consisting of hydrogen, alkyl, aryl and aralkyl; R is selected from the class consisting of alkyl, aryl, aralkyl and a cation; and n is a whole number of from 1 to 3.

6. The process as defined in claim 5 wherein the antifoggant is 1-phenyl-tetrazolyl-5-mercapto-acetic acid.

References Cited in the file of this patent UNITED STATES PATENTS Matthies May 13, 1930 Murray et a1. Jan. 14,1958 

1. LIGHT-SENSITIVE PHOTOGRAPHIC MATERIAL COMPRISING A BASE AND A LIGHT-SENSITIVE SILVER HALIDE EMULSION LAYER THEREON, A LAYER OF SAID PHOTOGRAPHIC MATERIAL CONTAINING AS AN ANTIFOGGANT A COMPOUND OF THE FOLLOWING FORMULA: 